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[Qemu-devel] [PATCH v2 2/1 for-2.6] nbd: Don't kill server when client r

From: Eric Blake
Subject: [Qemu-devel] [PATCH v2 2/1 for-2.6] nbd: Don't kill server when client requests unknown option
Date: Wed, 6 Apr 2016 16:48:38 -0600

nbd-server.c currently fails to handle unsupported options properly.
If during option haggling the client sends an unknown request, the
server kills the connection instead of letting the client try to
fall back to something older.  This is precisely what advertising
NBD_FLAG_FIXED_NEWSTYLE was supposed to fix.

Signed-off-by: Eric Blake <address@hidden>

Turns out our server has a very similar bug to the client.
If desired, I can spin a v3 that moves the hunk in nbd/client.c
to the previous patch.

 nbd/client.c | 2 ++
 nbd/server.c | 5 ++++-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/nbd/client.c b/nbd/client.c
index 67116b9..fc382c5 100644
--- a/nbd/client.c
+++ b/nbd/client.c
@@ -109,6 +109,8 @@ static int nbd_handle_reply_err(QIOChannel *ioc, uint32_t 
opt, uint32_t type,

     switch (type) {
     case NBD_REP_ERR_UNSUP:
+        TRACE("server doesn't understand request %d, attempting fallback",
+              opt);
         result = 0;
         goto cleanup;

diff --git a/nbd/server.c b/nbd/server.c
index b95571b..7843584 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -482,9 +482,12 @@ static int nbd_negotiate_options(NBDClient *client)
                 return -EINVAL;
                 TRACE("Unsupported option 0x%x", clientflags);
+                if (nbd_negotiate_drop_sync(client->ioc, length) != length) {
+                    return -EIO;
+                }
                 nbd_negotiate_send_rep(client->ioc, NBD_REP_ERR_UNSUP,
-                return -EINVAL;
+                break;
         } else {

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